1. Field of the Invention
The present invention relates generally to nuclear reactors, and more particularly to a new and improved replacement support pin and locking device system for utilization in connection with nuclear reactor control rod guide tubes within existing operating plants or facilities in order to fixedly secure the control rod guide tubes, by means of their annular flanged portions, to the upper surface of the upper core plate of the reactor by means of a non-welded mechanical system when existing, conventional welded guide tube support pin systems require replacement due to failure, for example, under stress corrosion cracking conditions.
2. Description of the Prior Art
As is well known, within a nuclear reactor, the upper boundary of the reactor core is defined by means of the upper core plate to the undersurface of which the upper ends of the nuclear reactor core fuel assemblies are connected. In addition to the core fuel assemblies being comprised of fuel rods within which the nuclear fuel pellets are disposed, each fuel assembly has defined therein numerous locations within hich nuclear reactor control rods are capable of being disposed for regulating the power output of the fuel assemblies and the reactor core. Control of the power output of the core fuel assemblies is in fact accomplished, for example, by regulating the disposition of the control rods with respect to the core, that is, lowering the same down into the core for decreasing the power output thereof, or elevating the control rods upwardly out of the core so as to permit an increase in the power output of the core. Elevational control of the nuclear reactor control rods is accomplished through means of control rod drive mechanisms (CRDMs) through the intermediary of control rod drive rods which pass vertically upwardly through the nuclear reactor pressure vessel to the uppermost region thereof within which they operatively connect to the control rod drive mechanisms which are actually located exteriorly of the nuclear reactor pressure vessel closure head.
Vertically spaced above the nuclear reactor upper core plate there is disposed the nuclear reactor upper support plate, and between the upper support plate and the upper core plate there is defined the upper plenum chamber through which nuclear reactor core coolant is conducted for subsequent flow through the reactor core coolant loop and heat exchange system which is external of the nuclear reactor pressure vessel and core barrel. In view of the fact that the nuclear reactor control rods may be disposed within the upper plenum chamber when, for example, particular control rods are withdrawn vertically upwardly out of the core, or alternatively, when the control rods are lowered into the core their respective drive rods will be disposed within the upper plenum chamber, protection for the control rods or their drive rods within the upper plenum chamber must be provided with respect to the cross-currents of the flowing nuclear reactor core coolant. Such protection is in fact provided through means of guide or shroud tubes which are interposed between, and fixedly connected to, the upper surface of the upper core plate and the upper support plate.
In particular, in connection with securing the guide tubes to the upper core plate, the guide tubes are provided with annular flanges at the lower ends thereof, and guide tube support pins fixedly interconnect the guide tube flanges to the upper core plate. The vertically disposed guide tube support pins have lower portions which are frictionally engaged within suitable bores defined within the upper core plate, and the upper bolt or stud portion of each guide tube support pin is threadedly engaged with a suitable, internal hexagonal nut, counterbored portions of the guide tube flange being retained between a shoulder portion of the support pin shank and the mated nut. In order to prevent the retrograde rotation of the nut relative to the support pin whereby the nut may possibly become disengaged from the threaded stud portion of the guide tube support pin, a dowel pin is conventionally passed through the nut and welded to a tab which is fixedly secured to the support pin.
While the aforenoted conventional guide tube support pin and locking system thereby fixedly secures the nuclear reactor control rod guide tubes within the upper core plate, stress corrosion cracking problems have been observed to have developed within the support pins leading to failure of the same. Consequently, the support pins require repair or replacement, however, due to the fact that such support pin and locking systems are now disposed within operating plants and are located in an irradiated, underwater environment, remotely controlled welding operations, in order to limit exposure of maintenance personnel to the irradiated environment, are extremely difficult to achieve, particularly in light of the small structural components which comprise the support pin and locking system, and the confined or restricted area within which the welding apparatus would have to be disposed and within which the welding operations would have to be performed and accomplished. In addition, while underwater welding operations per se have of course been capable of being conventionally performed, such conventional apparatus and techniques have only been able to be employed with high radiation dosage to personnel working under requisite remote control constraints. Consequently, in order to in fact be able to achieve such welding operations in connection with the repair or replacement of the failed and cracked guide tube support pin and locking systems, entirely new and technologically sophisticated underwater welding apparatus, including appropriate radiation shielding components, and associated techniques, would have to be developed. Such an undertaking is not deemed economically feasible and cost-effective, and in addition, such technological advances would require considerable time to be developed. A need therefore exists for an entirely different type of guide tube support pin and locking system.
Accordingly, it is an object of the present invention to provide a new and improved nuclear reactor guide tube support pin and locking system.
Another object of the present invention is to provide a new and improved nuclear reactor guide tube support pin and locking system which overcomes the various disadvantages and drawbacks characteristic of conventional guide tube support pin and locking sysems in connection with the installation and removal theroef.
Still another object of the present invention is to provide a new and improved nuclear reactor guide tube support pin and locking system which can effectively secure a nuclear reactor guide tube within the upper core plate and prevent disengagement therefrom by preventing retrograde rotation of the threaded locking nut by means of a non-welded locking system.
Yet another object of the present invention is to provide a new and improved nuclear reactor guide tube support pin and locking system which can effectively secure a nuclear reactor guide tube within the nuclear reactor upper core plate and prevent disengagement therefrom by preventing retrograde rotation of the threaded locking nut relative to the guide tube support pin by means of a simplified dual-crimp locking system.
Still yet another object of the present invention is to provide a new and improved nuclear reactor guide tube support pin and locking system which can effectively secure a nuclear reactor guide tube within the nuclear reactor upper core plate and prevent disengagement therefrom by preventing retrograde rotation of the threaded locking nut relative to the guide tube support pin by means of a simplified dual-crimp locking system which can be remotely implemented.
Yet still another object of the present invention is to provide a new and improved nuclear reactor guide tube support pin and locking system which can effectively secure a nuclear reactor guide tube within the nuclear reactor upper core plate and prevent disengagement therefrom by preventing retrograde rotation of the threaded locking nut relative to the guide tube support pin by means of a simplified dual-crimp locking cap system which can be remotely installed or removed.
A further object of the present invention is to provide a new and improved nuclear reactor guide tube support pin and locking system which can effectively secure a nuclear reactor guide tube within the nuclear reactor upper core plate and prevent disengagement therefrom by preventing retrograde rotation of the threaded locking nut relative to the guide tube support pin by means of a simplified dual-crimp locking cap system which can be remotely controlled within its underwater environment.
A yet further object of the present invention is to provide a new and improved nuclear reactor guide tube support pin and locking system which can effectively secure a nuclear reactor guide tube within the nuclear reactor upper core plate and prevent disengagement therefrom by preventing retrograde rotation of the threaded locking nut relative to the guide tube support pin by means of a simplified dual-crimp locking cap system which is extremely cost-effective to manufacture and to install or remove.
A still further object of the present invention is to provide a new and improved nuclear reactor guide tube support pin and locking system which can effectively secure a nuclear reactor guide tube within the nuclear reactor upper core plate and prevent disengagement therefrom by preventing retrograde rotation of the threaded locking nut relative to the guide tube support pin by means of a simplified dual-crimp locking cap system which can be remotely controlled within confined or restricted spacial environments.